This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-088448, filed on Mar. 26, 2001; the entire contents of which are incorporated herein by reference.
This invention relates to a magnetoresistive effect element, its manufacturing method, magnetic head, magnetic reproducing apparatus and magnetic memory, and more particularly, to a magnetoresistive effect element having a structure for carrying a sense current perpendicularly to the film plane thereof and applying a bias magnetic field to enable more sensitive detection than conventional elements of this kind, its manufacturing method, a magnetic head using the element, a magnetic reproducing apparatus using the magnetic head, and a magnetic memory using the magnetoresistive effect elements.
Magnetic reproducing devices such as hard disk devices have rapidly moved toward downsizing and high densities, and are still expected to become higher in density. For realizing higher densities in magnetic recording technologies, it is necessary to increase the lengthwise recording density, i.e. line recording density, in addition to increasing the recording track density by narrowing the recording track width.
However, in the xe2x80x9clengthwise recording methodxe2x80x9d that magnetizes a medium in its lengthwise direction, as the recording density increases, the demagnetizing field increases, and it results in decreasing the reproduction output and disabling stable recording. To alleviate these problems, xe2x80x9cperpendicular magnetic recordingxe2x80x9d has been proposed. Perpendicular magnetic recording is a method of magnetizing a recording medium perpendicularly to its plane for recording, and has the advantage of less adverse influences of demagnetization even under a high recording density than the lengthwise recording and a less decrease of the reproduction output.
For reproduction of signals from mediums, either in the lengthwise recording or in the perpendicular recording, magnetic induction heads have been used conventionally. However, along with progressive increases of the recording density, the recording track width becomes narrower, and the intensity of recorded magnetization becomes weaker. Taking it into account, toward obtaining a sufficient reproduction output by detecting such weak magnetization, an AMR (anisotropic magnetoresistive effect) head using anisotropic magnetoresistive effect and having a high reproduction sensitivity has been developed and brought into practical use as a shield type reproducing head. Additionally, a spin valve GMR (giant magnetoresistive effect) head using GMR effect and having a higher sensitivity has recently come to be used, and magnetic heads using TMR (tunneling magnetoresistive) effect are also under researches toward development and practical use.
By development and employment of these magnetic heads, a clue to reproduction of recording signals was found even with very small recording bit sizes.
As the recording density increases, the sensitivity of the sensor must be higher. CPP (current perpendicular to the plane) type GMR elements meet such requirement. This is an element of the type supplying the GMR film having a multi-layered thin film structure with a sense current for detection of a magnetic field to the perpendicularly to the film plane.
CPP elements are disclosed in, for example, Japanese Patent Laid-Open Publication No. H10-55512 and U.S. Pat. No. 5,668,688.
On the other hand, there is a method that, for the purpose of suppressing the Barkhausen noise, places bias films at opposite ends and applies a bias magnetic field from the bias films. The Inventors, however, have found that narrowing the distance between the bias-applying films along with progressive decrease of the track width for the purpose of increasing the recording density results in applying an excessively high bias magnetic field and in decreasing the sensitivity of the element.
Neither Japanese Patent Laid-Open Publication No. H10-55512 nor U.S. Pat. No. 5,668,688 mentioned above suggests that problem, and it is difficult for the configurations disclosed therein to sufficiently overcome the problem.
On the other hand, for realizing highly sensitive CPP type GMR elements, the sense current has to flow as perpendicular as possible to the film plane. However, since these highly sensitive MR elements are usually made of a multi-layered film different in resistance, the current profile changes depending on the combination of the layers including the base layer, protective layer and electrode layer, and results in fluctuation of the output. Therefore, control of the current profile is very important.
Additionally, in case of flowing the sense current perpendicularly to the film plane, a magnetic field caused by the sense current is added concentrically around the current center. This magnetic field caused by the sense current is most intensive at an end of the electrode supplying the sense current, and saturates the magnetic shield near there. There occurs the problem that the effective shield distance increases.
It is therefore an object of the invention to provide a CPP type magnetoresistive effect element having bias-applying films and enabling high-density, high-sensitivity magnetic detection, and its manufacturing method, and to provide a magnetic head, magnetic reproducing device and magnetic memory such as MRAM, which use the magnetoresistive effect element.
To accomplish the object, a magnetoresistive effect element according to an embodiment of the invention comprises:
a magnetoresistive effect film having first and second main surfaces opposed to each other;
a first electrode having a first contact surface in contact with the first main surface of the magnetoresistive effect film by a first width;
a second electrode having a second contact surface in contact with the second main surface of the magnetoresistive effect film so as to be opposed to the first electrode; and
a pair of bias-applying films spaced apart by a distance wider than the first width of the first contact surface in the direction of the first width to apply a bias magnetic field in a direction substantially in parallel to the film main surfaces of the magnetoresistive effect film.
As explained above, according to the embodiments of the invention, a high sensitivity can be realized in a CPP type magnetoresistive effect element even under a high recording density by supplying the sense current exclusively to the inner portion having a high sensitivity, avoiding portions near the bias-applying films where the sensitivity is lowered by the intensive bias magnetic field.